Semiconductor device and method of manufacturing the same

ABSTRACT

A semiconductor device includes a cell structure; n first pad structures formed on one side of the cell structure and each configured to have a step form in which 2n layers form one stage; and n second pad structures formed on the other side of the cell structure each configured to have a step form in which 2n layers form one stage, wherein n is a natural number of 1 or higher, and the first pad structures and the second pad structures have asymmetrical step forms having different heights.

CROSS-REFERENCE TO RELATED APPLICATION

The present application claims priority to Korean patent applicationnumber 10-2012-0074919 filed on Jul. 10, 2012, in the KoreanIntellectual Property Office, the entire disclosure of which isincorporated by reference herein.

BACKGROUND

Field of Invention

Embodiments of this disclosure relate to a semiconductor device and amethod of manufacturing the same and, more particularly, to athree-dimensional (3-D) semiconductor device including pad structuresand a method of manufacturing the same.

Description of the Related Art

A nonvolatile memory device retains stored data although the supply ofpower to the device may be cut-off. As the degree of integration of 2-Dstructured memory devices including memory cells fabricated on a singlelayer of a silicon substrate is approaching a limit, a 3-D structurednonvolatile memory device has been proposed. The 3-D nonvolatile memorydevice typically includes memory cells that are vertically stacked on asilicon substrate.

In this 3-D nonvolatile memory device, desired memory cells are drivenby supplying biases to respective word lines stacked in multiple layersover a substrate. To drive memory cells by supplying biases torespective word lines, a pad unit is formed for each word line bypatterning the word lines, formed in a slimming region, in a step form.Furthermore, contact plugs and metal lines coupled to the respectiveword lines are formed so that the word lines stacked in multiple layersmay be controlled.

FIG. 1 is a perspective view showing a structure of a known 3-Dnonvolatile memory device. For ease of description, only a cellstructure and pad structures are illustrated in FIG. 1.

As shown in FIG. 1, the known 3-D nonvolatile memory device includes acell region CR and first and second slimming regions SR1 and SR2 placedon both sides of the cell region CR.

The cell structure C placed in the cell region CR includes channellayers CH configured to penetrate the cell structure C in a stackdirection.

Pad structures P1 and P2 are formed in the slimming regions SR1 and SR2.Each of the pad structures P1 and P2 includes a step form in which onelayer forms one stage. In order to form these pad structures, afterforming word lines stacked in multiple layers, an etch process isrepeatedly performed while reducing one mask pattern.

In a structure, such as that described above, the pad structures P1 andP2 are formed in a step form in which one layer forms one stage.Accordingly, the slimming regions SR1 and SR2 become wide, and animprovement in the degree of integration of memory devices is limited.Furthermore, in order to form n layers of the pad structures P1 and P2in a step form, n etch processes must be performed, thereby increasingthe complexity of the etching process.

BRIEF SUMMARY

An example embodiment of this disclosure relates to a semiconductordevice suitable for a simplified slimming process and a method ofmanufacturing the same.

In an embodiment of this disclosure, a semiconductor device includes acell structure; n first pad structures formed on one side of the cellstructure and each configured to have a step form in which 2n layersform one stage; and n second pad structures formed on the other side ofthe cell structure each configured to have a step form in which 2nlayers form one stage, wherein n is a natural number of 1 or higher, andthe first pad structures and the second pad structures have asymmetricalstep forms having different heights.

In another embodiment of this disclosure, a method of manufacturing asemiconductor device includes forming a stack structure in which a cellregion and slimming regions placed on opposite sides of the cell regionare defined; performing a primary slimming process of selectivelyetching the slimming regions of the stack structure to form a cellstructure and n first pad structures and n second pad structures placedon opposite sides of the cell structure, wherein the slimming regionsare selectively etched so that steps are formed between the first andthe second pad structures; and performing a secondary slimming processof forming a mask pattern through which the ends of the first and thesecond pad structures are exposed over the stack structure and etching2n layers of the first and the second pad structures using the maskpattern as an etch barrier so that each of the first and the second padstructures has a step form in which 2n layers form one stage, whereinthe n is a natural number of 1 or higher.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a perspective view showing a structure of a known 3-Dnonvolatile memory device;

FIG. 2 is a perspective view showing a structure of a semiconductordevice in accordance with an embodiment of this disclosure;

FIGS. 3A to 6B are diagrams illustrating a method of manufacturing thesemiconductor device in accordance with an embodiment of thisdisclosure;

FIG. 7 is a perspective view showing a structure of a semiconductordevice in accordance with an embodiment of this disclosure;

FIGS. 8A to 12B are diagrams illustrating the method of manufacturingthe semiconductor device in accordance with an embodiment of thisdisclosure;

FIGS. 13 to 15 are perspective views showing the cell structure of asemiconductor device to which embodiments of this disclosure have beenapplied;

FIG. 16 shows a construction of a memory system in accordance with anexample embodiment of this disclosure; and

FIG. 17 shows a construction of a computing system in accordance with anexample embodiment of this disclosure.

DESCRIPTION OF EMBODIMENTS

Hereinafter, some example embodiments of the present disclosure will bedescribed in detail with reference to the accompanying drawings. Thefigures are provided to provide those having ordinary skill in the artto understand the scope of the embodiments of the disclosure.

FIG. 2 is a perspective view showing a structure of a semiconductordevice in accordance with an embodiment of this disclosure. For ease ofdescription only a cell structure and pad structures are illustrated inFIG. 2.

As shown in FIG. 2, the semiconductor device in accordance with anembodiment of this disclosure includes a cell structure C and first andsecond pad structures P11 to P22. The cell structure C and the first andthe second pad structures P11 to P22 are formed by selectively etchingone stack structure. Accordingly, the cell structure C and the first andthe second pad structures P11 to P22 are formed in such a way as to beinterconnected. In this specification, for ease of description the cellstructure C and the first and the second pad structures P11 to P22 aredivided and defined according to their regions.

The cell structure C is formed in a cell region CR. The cell structure Cincludes interlayer insulating layers and conductive layers which arealternately stacked. The cell structure C may further include channellayers CH configured to penetrate the interlayer insulating layers andthe conductive layer in the stack direction.

First pad structures P11 and P12 are placed in a first slimming regionSR1 and are coupled to one side of the cell structure C. A number n (forexample, n=2) of the first pad structures P11 and P12 are formed in thefirst slimming region SR1. Here, n is a natural number of 1 or higher.Each of the first pad structures P11 and P12 has a step form in which 2n(for example, 2n=4) layers may form one stage. However, in someembodiments, in view of a characteristic of this disclosure that theremay be a step between the first and the second pad structures P11 toP22, the highest stage and lowest stages of each of the pad structureP11 to P22 may include fewer layers than 2n (for example, 2n=4) layers.

Second pad structures P21 and P22 are placed in a second slimming regionSR2 and are coupled to an other side of the cell structure C. Forexample, the second pad structures P21 and P22 are placed on theopposite side of the cell structure C as the first pad structures P11and P12, with the cell structure C interposed between them. A number n(for example, n=2) of the second pad structures P21 and P22 are formedin the second slimming region SR2. Furthermore, each of the second padstructures P21 and P22 has a step form in which 2n (for example, 2n=4)layers form one stage.

Each of the layers of the first and the second pad structures P11 to P22includes a stack of an interlayer insulating layer and a conductivelayer and may include an upper interlayer insulating layer and a lowerconductive layer, or an upper conductive layer and a lower interlayerinsulating layer. For example, if the first and the second padstructures P11 to P22 include first conductive layers and firstinterlayer insulating layers alternately stacked, and the cell structureC includes second conductive layers and second interlayer insulatinglayers alternately stacked, the first conductive layer and the secondconductive layer of a substantially same level may be coupled, and thefirst interlayer insulating layer and the second interlayer insulatinglayer of a substantially same level may be coupled.

Furthermore, the first and the second pad structures P11 to P22 haverespective step forms each having steps formed in opposite directions inrelation to the cell structure C. In other words, each of the first andthe second pad structures P11 to P22 has a form in which a step isformed in a first direction I-I′, and the first pad structures P11 andP12 and the second pad structures P21 and P22 have steps formed inopposite directions. For example, when viewing the first and second padstructures P11 to P22 in the direction from I′ to I, the step of thefirst pad structures P11 and P12 may ascend and the second padstructures P21 and P22 may descend.

Furthermore, the first pad structures P11 and P12 adjacent to each otherin a second direction II-II′ have a step of one layer, and the secondpad structures P21 and P22 adjacent to each other in the seconddirection II-II′ also have a step of one layer. Furthermore, each of thepair of first and the second pad structures P12 and P21 placed onopposite sides of the cell structure C and the pair of first and secondpad structures P11 and P22 placed on opposite sides of the cellstructure C has n (for example, n=2) layers of steps. Accordingly, thefirst pad structures P11 and P12 have an asymmetrical structure, thesecond pad structures P21 and P22 have an asymmetrical structure, thefirst pad structures P11 and P12 and the second pad structures P21 andP22 also have an asymmetrical structure.

In a structure, such as that described above, the first and the secondslimming regions SR1 and SR2 are defined on opposite sides of the cellregion CR. Furthermore, the first slimming region SR1 is split into n(for example, n=2), and n of the first pad structures are formed in thesplit slimming regions. The second slimming region SR2 is split into n(for example, n=2), and n (for example, n=2) number of the second padstructures are formed in the split regions. In particular, the first padstructures and the second pad structures have an asymmetrical step formhaving steps. When a number of the pad structures are formed in anasymmetrical step form as described above, the area of the slimmingregion can be reduced as compared with a known art.

FIGS. 3A to 6B are diagrams illustrating a method of manufacturing thesemiconductor device in accordance with the embodiment of thisdisclosure as seen in FIG. 2. An ‘a’ figure of each of FIGS. 3 to 6 is alayout diagram, and a ‘b’ figure of each of FIGS. 3 to 6 shows aperspective view.

As shown in FIGS. 3A and 3B, a stack structure is formed in which thecell region CR and the first and the second slimming regions SR1 and SR2placed on opposite sides of the cell region CR are defined. Here, thefirst slimming region is a region in which n (for example, n=2) numberof the first pad structures P11 and P12 will be formed, and the secondslimming region is a region where n (for example, n=2) number of thesecond pad structures P21 and P22 will be formed.

The stack structure may be formed by alternately stacking first materiallayers 1 and second material layers 2. Here, the second material layer 2on the upper side and the first material layer 1 on the lower side formone layer (11 to 19), and the stack structure includes multiple layers.

In an embodiment, the second material layer 2 and the first materiallayer 1, which are stacked on top of each other, are illustrated asforming one layer (11 to 22), and the case where the stack structureincludes a total of m (for example, m=12; 11 to 22) layers is describedbelow.

For example, the first material layers 1 and the second material layers2 may be alternately stacked over a substrate in which underlyingstructures, such as a source region, are formed, thus forming the stackstructure. Here, the first material layers 1 are used to form conductivelayers for word lines or selection lines, and each of the secondmaterial layers 2 is used to separate the stacked conductive layers fromeach other. The first material layers 1 may be formed with differentthicknesses according to the intended use of the material layer. Forexample, the conductive layers for selection lines may have the samethickness as or thicker than the conductive layers for word lines.

Furthermore, the first material layer 1 and the second material layer 2are made of materials having a high etch selectivity. For example, thefirst material layer 1 may be formed of a conductive layer, such as apolysilicon layer, and the second material layer 2 may be formed of aninsulating layer, such as an oxide layer. In another example, the firstmaterial layer 1 may be formed of a conductive layer, such as a dopedpolysilicon layer or a doped amorphous silicon layer, and the secondmaterial layer 2 may be formed of a sacrificial layer, such as anundoped polysilicon layer or an undoped amorphous silicon layer. In yetanother example, the first material layer 1 may be formed of asacrificial layer, such as a nitride layer, and the second materiallayer 2 may be formed of an insulating layer, such as an oxide layer.

As shown in FIGS. 4A to 5B, a primary slimming process of defining thecell structure C and the pad structures P11 to P22 by selectivelyetching the slimming regions of the stack structure is performed.

First, as shown in FIGS. 4A and 4B, after forming a first mask pattern23 such that regions where the pair of first and second pad structuresP11 and P21 remain exposed, one layer 22 that consists of the first andthe second pad structures P11 and P21 is etched using the first maskpattern 23 as an etch barrier.

Accordingly, a step is formed between the pad structures P11 and P12placed in the same slimming region, and a step is formed between the padstructures P21 and P22 placed in the same slimming region. That is, astep is formed between the first pad structures P11 and P12 adjacent toeach other in the second direction II-II′, and a step is formed betweenthe second pad structures P21 and P22 adjacent to each other in thesecond direction II-II′.

At this point, the first and the second pad structures P11 and P21placed on opposite sides of the cell structure C and the first and thesecond pad structures P12 and P22 placed on opposite sides of the cellstructure C have a symmetrical structure. That is, the first and thesecond pad structures P11 and P21 have a form in which one layer hasbeen etched, and the first and the second pad structures P12 and P22have a form in which none of the layers have been etched. In order tohelp understanding, the number of layers etched in each pad structure isshown within a circle in the layout diagram of FIG. 4A.

Next, as shown in FIGS. 5A and 5B, after forming a second mask pattern24 such that the second pad structures P21 and P22 remain exposed, n(for example, n=2) layers of the second pad structures are etched byusing the second mask pattern 24 as an etch barrier. Here, n (forexample, n=2) layers of the second pad structures P21 and P22 are etchedfrom the top while maintaining a step therebetween. For example, twolayers 20 and 21 at the top of the second pad structure P21 are etched,and two layers 21 and 22 at the top of the second pad structure P22 areetched, so that the step is maintained between the second pad structuresP21 and P22.

In some embodiments, the second mask pattern 24 may be formed such thatthe first pad structures P11 and P12 remain exposed.

As a result, a step is formed between the first and the second padstructures P11 and P21 placed on opposite sides of the cell structure C,and a step is formed between the first and the second pad structures P12and P22 placed on opposite sides of the cell structure C. Accordingly, astep is formed between all the first and the second pad structures P11to P22.

After the primary slimming process is completed, there is a step notonly between the first and the second pad structures P11 to P22 adjacentto each other in the second direction II-II′, but also between the firstand the second pad structures P11 to P22 placed on opposite sides of thecell structure C in the first direction I-I′. In some embodiments, afterforming a step between the first and the second pad structures P11 toP22 placed on opposite sides of the cell structure C, a step may beformed between the first and the second pad structures P11 to P22adjacent to each other in the second direction II-II′.

As shown in FIGS. 6A and 6B, a secondary slimming process of patterningthe first and the second pad structures P11 to P22 in a step form isperformed.

First, a third mask pattern 25 is formed such that ends of the first andthe second pad structures P11 to P22 in the first direction I-I′ remainexposed, the third mask pattern 25 may be formed over the stackstructure on which the primary slimming process has been completed. Thethird mask pattern 25 is formed to have a size such that the ends of thefirst and the second pad structures P11 to P22 that remain exposed havea width equal to the pad unit of the first material layer 1 included ineach layer. Furthermore, the third mask pattern 25 is formed to be thickenough to function as an etch barrier although the third mask pattern 25may be reduced in a subsequent etch process.

2n (for example, 2n=4) layers are etched by using the third mask pattern25 as an etch barrier. Here, a step between the first and the second padstructures P11 to P22 remains intact, and the stack structure is etchedby 2n (for example, 2n=4) layers from the tops of the first and thesecond pad structures P21 to P22.

Next, the third mask pattern 25 is reduced. The third mask pattern 25 isreduced by a width equal to the pad unit of the first material layer 1included in each layer in the first direction I-I′. Accordingly, thefirst and the second pad structures P11 to P22 are extended in adirection away from the cell structure C, i.e., in the first I-I′direction, thus being patterned in a step form, such that the steps ofeach first and second pad structures P11 to P22 descend as the stepsextend away from the cell structure C. For example, if the cellstructure C is placed in the direction I on the basis of the first padstructures P11 and P12, the first pad structures P11 and P12 arepatterned to have a step while extending in the direction I′.Furthermore, if the cell structure C is placed in the direction I′ onthe basis of the second pad structures P21 and P22, the second padstructures P21 and P22 are patterned to have a step while extending inthe direction I.

In some embodiments, the first material layers 1 included in each layermay have pad units having the same width or the pad units havingdifferent widths. For example, the first material layer 1 on the lowerside may have the pad unit having a wider width by taking an alignmentmargin of contact plugs and pad units formed in a subsequent processinto consideration. In this case, the decrement of the width is reducedwhenever the third mask pattern 25 is reduced.

Next, 2n (for example, 2n=4) layers are etched by using the third maskpattern 25 as an etch barrier. Here, the first etched 2n (for example,2n=4) layers at the top and 2n (for example, 2n=4) layers under thefirst etched 2n layers are etched at the same time. The processes ofreducing the third mask pattern 25 and etching the 2n layers asdescribed above are repeated until a total of m (for example, m=12)layers are etched.

As a result, the first and the second pad structures P11 to P22 eachhaving a step form in which the 2n (for example, 2n=4) layers form onestage are formed. For example, the first pad structure P11 is patternedin a step form having 3 stages 11 to 13, 14 to 17, and 18 to 21, and thefirst pad structure P12 is patterned in a step form having 3 stages 11to 14, 15 to 18, and 19 to 22. Furthermore, the second pad structure P21is patterned in a step form having 3 stages 11, 12 to 15, and 16 to 19,and the second pad structure 22 is patterned in a step form having 3stages 11 to 12, 13 to 16, and 17 to 20.

In some embodiments, after performing the secondary slimming process,the primary slimming process may be performed.

Next, a process of forming the memory cells of the cell structure isperformed although (not shown). For example, after forming channellayers penetrating the cell structure C, an insulating layer may befilled within slits. Thus, the memory cells stacked in the cell regionCR are formed.

After forming the slits, an additional process may be performeddepending on the type of first material layers 1 and second materiallayers 2.

For example, the first material layer 1 may be a conductive layer, andthe second material layer 2 may be formed of an insulating layer. Inthis case, after siliciding the first material layers 1 that remainexposed within the slits, an insulating layer is filled within theslits.

Here, an air gap may be formed within the slits depending on a method ofdepositing the insulating layer.

For another example, the first material layer 1 may be formed of aconductive layer, and the second material layer 2 may be formed of asacrificial layer. In this case, after removing the second materiallayers 2 exposed within the slits, an insulating layer is filled withinthe regions from which the second material layers 2 have been removedand within the slits. Here, an air gap may be formed within the regionsfrom which the second material layers 2 have been removed and within theslits depending on a method of depositing the insulating layer.

For yet another example, the first material layer 1 may be formed of asacrificial layer, and the second material layer 2 may be formed of aninsulating layer. In this case, the second material layers 2 exposedwithin the slits are removed. Next, word lines and selection lines areformed by filling a conductive layer made of tungsten (W) within theregions from which the first material layers 1 have been removed. Next,an insulating layer 40 (see FIG. 8B) is filled within the slits.

In accordance with the above method, the slimming process can besimplified as compared with a known method because the pad structure ispatterned in a step form in which 2n (2n=4) layers form one stage.

FIG. 7 is a perspective view showing the structure of a semiconductordevice in accordance with a second embodiment of this disclosure. Forease of description, only a cell structure and pad structures areillustrated in this figure. For purposes of brevity, descriptions thatare substantially similar to the descriptions given in connection withthe embodiment shown in FIG. 2 are omitted.

As shown in FIG. 7, a semiconductor device in accordance with anembodiment of this disclosure includes a cell structure C placed in acell region CR and first and second pad structures P11 to P23 placed infirst and second slimming regions SR1 and SR2. The first and the secondslimming regions SR1 and SR2 include n (for example, n=3) pad structuresP11 to P13 and P21 to P23, respectively, and each of the pad structuresP11 to P23 has a step form in which 2n (for example, 2n=6) layers mayform one stage.

FIGS. 8A to 12B are diagrams illustrating a method of manufacturing thesemiconductor device in accordance with the embodiment of thisdisclosure shown in FIG. 7. An ‘a’ figure of each of FIGS. 8 to 12 is alayout diagram, and ‘b’ and ‘c’ figures of each of FIGS. 8 to 12 showperspective views. Contents redundant with descriptions given inrelation to previous embodiments are omitted, for simplicity.

As shown in FIGS. 8A and 8B, a stack structure is formed in which thecell region CR and the first and the second slimming regions SR1 andSR2, placed on opposite sides of the cell region CR, are defined. Thefirst and the second slimming regions SR1 and SR2 are regions where then (for example, n=3) pad structures P11 to P23 will be formed.Furthermore, the stack structure is formed of m (for example, m=18; 31to 48) layers.

As shown in FIGS. 9A to 10B, a step is formed between the pad structuresP11, P12, and P13 placed in the same slimming region, and a step isformed between the pad structures P21, P22, and P23 placed in the sameslimming region.

As shown in FIGS. 9A and 9B, there is formed a first mask pattern (notshown) such that regions where the pair of first and second padstructures P11 and P21 will be formed remain exposed. One layer 48 ofthe first and the second pad structures P11 and P21 is etched using thefirst mask pattern as an etch barrier.

Next, as shown in FIGS. 10A and 10B, the first mask pattern is reducedin a second direction II-II′ so that the pair of first and second padstructures P12 and P22 placed on opposite sides of the cell structure Care exposed. One layer (47 and 48) that consists of the first and thesecond pad structures P11 to P22 is etched using the reduced first maskpattern as an etch barrier. At this time, the one layer 47 of the firstand the second pad structures P11 and P21 first etched and the one layer48 of the first and the second pad structures P12 and P22 newly exposedare etched at the same time, so the first and the second pad structuresP11 and P21 maintain a step of one layer.

Accordingly, a step is formed between the pad structures P11, P12, andP13 placed in the same slimming region, and a step is formed between thepad structures P21, P22, and P23 placed in the same slimming region.Here, the processes of reducing and etching the first mask pattern isrepeated until a step is formed between the pad structures P11, P12, andP13 placed in the first slimming region SR1 and between the padstructures P21, P22, and P23 placed in the second slimming region SR2.For example, if each of the first and the second slimming regions SR1and SR2 includes n pad structures, an etch process may be performed(n−1) times while reducing the first mask pattern.

As shown in FIGS. 11A and 11B, after forming a second mask pattern (notshown) such that the second pad structures P21 to P23 remain exposed, n(for example, n=3) layers of the second pad structures P21 to P23 areetched using the second mask pattern as an etch barrier.

Thus, a step is formed between all the first and the second padstructures P11 to P33, and thus the primary slimming process iscompleted.

As shown in FIGS. 12A and 12B, a third mask pattern (not shown) suchthat the ends of the first and the second pad structures P11 to P23 in afirst direction I-I′ remain exposed is formed on the results on whichthe primary slimming process has been completed. 2n (for example, 2n=6)layers at the top are etched using the third mask pattern as an etchbarrier. The step between the first and the second pad structures P11 toP23 remains intact, and the 2n (for example, 2n=6) layers at the top areetched.

After reducing the third mask pattern, the 2n (for example, 2n=6) layersare etched using the reduced third mask pattern as an etch barrier.Here, the 2n (for example, 2n=6) layers first etched at the top and 2n(for example, 2n=6) layers under the 2n (for example, 2n=6) layers areetched at the same time. The process of etching the 2n (for example,2n=6) layers after reducing the third mask pattern is repeatedlyperformed until a total of m (for example, m=18) layers are fullypatterned.

As a result, the first and the second pad structures P11 to P23 areformed, such that each of the first and second pad structures P11 to P23each may have a step form in which the 2n (for example, 2n=6) layersform one stage. For example, the first pad structure P11 is patterned ina step form having 3 stages 31 to 34, 35 to 40, and 41 to 46; the firstpad structure P12 is patterned in a step form having 3 stages 31 to 35,36 to 41, and 42 to 47; and the first pad structure P13 is patterned ina step form having 3 stages 31 to 36, 37 to 42, and 43 to 48.Furthermore, the second pad structure P21 is patterned in a step formhaving stages 31, 32 to 37, and 38 to 43; the second pad structure P22is patterned in a step form having 3 stages 31 to 32, 33 to 38, and 39to 44; and the second pad structure P23 is patterned in a step formhaving 3 stages 31 to 33, 34 to 39, and 40 to 45.

FIG. 13 is a perspective view showing the cell structure of asemiconductor device to which embodiments of this disclosure has beenapplied. For ease of description, an insulating layer is not shown.

As shown in FIG. 13, the semiconductor device in accordance with anexample embodiment of this disclosure includes at least one layer of alower selection line LSL, multiple layers of word lines WL, and at leastone layer of an upper selection line USL which are sequentially stackedover a substrate SUB equipped with a source region S. The semiconductordevice further includes vertical channel layers CH configured topenetrate the lower selection line LSL, the word lines WL, and the upperselection line USL, a memory layer (not shown) configured tosubstantially surround the vertical channel layers CH, and bit lines BLextended in a second direction II-II′. The bit lines B are coupled tothe tops of the vertical channel layers CH arranged in the seconddirection II-II′.

FIG. 14 is a perspective view showing the cell structure of asemiconductor device to which embodiments of this disclosure has beenapplied. For ease of description, an insulating layer is not shown.

As shown in FIG. 14, the semiconductor device in accordance with anexample embodiment of this disclosure includes a first source layer S1,one or more second source layers S2 formed within the first source layerS1, conductive layers (LSL, WL, USL) stacked over the first source layerS1 in multiple layers, semiconductor pillars configured to penetrate theconductive layers and coupled to the second source layers S2, and thirdsource layers S3 formed within the second source layers S2,respectively, configured to penetrate the second source layers S2, andcoupled to the first source layer S1.

The semiconductor device further includes a memory layer (not shown)configured to substantially surround the outer surfaces of thesemiconductor pillars and the second source layers S2 and bit lines BLformed at the tops of the conductive layers and extended in a seconddirection II-II′. The bit lines BL are coupled to respectivesemiconductor pillars arranged in the second direction II-II′.

From among the conductive layers stacked in multiple layers, one or moreconductive layers at the bottom may be used as lower selection linesLSL, one or more conductive layers at the top may be used as upperselection lines USL, and the remaining conductive layers may be used asword lines WL.

Each of the first to third source layers S1 to S3 may be formed of apolysilicon layer or a metal layer into which an impurity has beendoped. For example, each of the first and the second source layers S1and S2 may be formed of a polysilicon layer into which an N typeimpurity has been doped, and the third source layer S3 may be formed ofa metal layer made of tungsten (W).

The semiconductor pillar may be used as channel layers CH. For example,the semiconductor pillar may be formed of a polysilicon layer into whichan impurity has not been doped. Furthermore, the semiconductor pillarsmay be integrally coupled to the second source layers S2.

A method of manufacturing the semiconductor device having the abovestack structure is described below. Before forming the stack structure,the first source layer S1 is formed. After forming trenches T by etchingthe first source layer S1, a sacrificial layer (not shown) is formedwithin the trenches. The trenches T may be formed in an area where thesecond and third source layers S2 and S3 are formed. Channel holes Hcoupled to the trenches T are formed over the first source layer S1 inwhich the sacrificial layer is formed, by etching first material layersand second material layers. The sacrificial layer exposed at the bottomof the channel holes H is removed. Next, a semiconductor layer is formedon the inside of the trenches T and the channel holes H. A first slitSL1 having a depth extended down to the first source layer S1 is formedbetween the channel holes H above an area where the third source layerS3 may be formed. An impurity is doped into the semiconductor layersformed within the trenches T through the first slits SL1, therebyforming the second source layers S2. Next, the third source layers S3coupled to the first source layer S1 are formed within the second sourcelayers S2 and a lower portion of the first slits SL1.

FIG. 15 is a perspective view showing the cell structure of asemiconductor device to which embodiments of this disclosure has beenapplied. For ease of description, an insulating layer is not shown.

As shown in FIG. 15, the semiconductor device in accordance with anexample embodiment of this disclosure includes an interlayer insulatinglayer ILD, one or more first source layers S1 formed within theinterlayer insulating layer ILD, conductive layers (LSL, WL, USL)stacked in multiple layers over the interlayer insulating layer ILD,semiconductor pillars configured to penetrate the conductive layers andcoupled to the first source layers S1, and second source layers S2formed within the first source layers S1, respectively. Thesemiconductor device further includes a memory layer (not shown)configured to substantially surround the outer surfaces of thesemiconductor pillars and the first source layer S1 and bit lines BLformed over the conductive layers and extended in a second directionII-II′.

Here, the semiconductor pillars may be used as channel layers CH, andthe conductive layers may be used as lower selection lines LSL, wordlines WL, or upper selection lines USL.

Furthermore, the first source layer S1 may be formed by doping animpurity into the semiconductor layer, and the second source layer S2may be formed of a metal layer. In this case, the characteristics of thesemiconductor device can be improved because source resistance isreduced.

In FIG. 15, the first source layer S1 is illustrated as fullysurrounding the bottom of the second source layer S2. In someembodiments, the bottom of the second source layer S2 may be partiallyprotruded so that the protruded part penetrates the first source layerS1.

A method of forming the cell structure of the semiconductor devicehaving the above stack structure is described below. Before forming thestack structure, the interlayer insulating layer ILD is formed. Next,trenches T are formed by etching the interlayer insulating layer ILD.The trenches T may be formed in an area where the first and secondsource layers S1 and S2 are formed. After forming a sacrificial layer(not shown) within the trenches T, first material layers and secondmaterial layers are alternately formed over the interlayer insulatinglayer in which the sacrificial layer is formed. Channel holes H coupledto the trenches T are formed by etching the first material layers andthe second material layers. Next, the sacrificial layer exposed at thebottom of the channel holes is removed. Next, a semiconductor layer isformed on the inside of the trenches T and the channel holes H. Next, afirst slit SL1 having a depth extended down to at least the trenches Tis formed between the channel holes H. An impurity is doped into thesemiconductor layers formed within the trenches T through the firstslits SL1, thereby forming the first source layers S1. The second sourcelayers S2 are formed within the first source layers S1, respectively.

FIG. 16 shows a construction of a memory system in accordance with anexample embodiment of this disclosure.

As shown in FIG. 16, the memory system 100 in accordance with an exampleembodiment of this disclosure includes a nonvolatile memory device 120and a memory controller 110.

The nonvolatile memory device 120 is configured to have a memory cellincluding the pad structures described in connection with the first orsecond embodiment. Furthermore, the nonvolatile memory device 120 may bea multi-chip package including a plurality of flash memory chips.

The memory controller 110 is configured to control the nonvolatilememory device 120, and it may include SRAM 111, a Central ProcessingUnit (CPU) 112, a host interface (I/F) 113, an ECC circuit 114, and amemory interface (I/F) 115. The SRAM 111 is used as the operating memoryof the CPU 112. The CPU 112 performs an overall control operation fordata exchange of the memory controller 110. The host I/F 113 is equippedwith the data exchange protocol of a host that accesses the memorysystem 100. Furthermore, the ECC 114 circuit detects and corrects errorsincluded in data read from the nonvolatile memory device 120. The memoryI/F 115 performs as an interface for the nonvolatile memory device 120.The memory controller 110 may further include RCM for storing code datafor an interface with the host.

The memory system 100 configured as described above may be a memory cardor a Solid State Disk (SSD) in which the nonvolatile memory device 120and the controller 110 are combined. For example, if the memory system100 is an SSD, the memory controller 110 may communicate with theoutside (for example, a host) through one of various interfaceprotocols, such as USB, MMC, PCI-E, SATA, PATA, SCSI, ESDI, and IDE.

FIG. 17 shows a construction of a computing system in accordance with anexample embodiment of this disclosure.

As shown in FIG. 17, the computing system 200 according to an embodimentof this disclosure may include a CPU 220, RAM 230, a user interface 240,a modem 250, and a memory system 210 all of which are electricallycoupled to a system bus 260. If the computing system 200 is a mobiledevice, the computing system 200 may further include a battery forsupplying operating voltages to the computing system 200. The computingsystem 200 may further include application chipsets, a Camera ImageProcessor (CIS), mobile DRAM, and so on.

The memory system 210 may include a non-volatile memory device 212 and amemory controller 211, such as those described above with reference toFIG. 16.

In this disclosure, a nonvolatile memory device, particularly, a 3-DNAND flash device in which word lines are stacked has been described asan example, but this disclosure is not limited thereto. This disclosuremay be applied to all semiconductor devices including stacked conductivelayers and may also be applied to volatile memory devices, such as DRAM,and nonvolatile memory devices, such as RERAM and PCRAM.

As described above, the semiconductor device includes a plurality of padstructures placed on opposite sides of a cell structure. Here, the padstructures have asymmetrical step forms. Accordingly, the area of aslimming region can be reduced and a slimming process can be simplifiedas compared with a known art.

What is claimed is:
 1. A semiconductor device, comprising: a cellstructure; n first pad structures, each having a step form in which 2nlayers form one stage; and n second pad structures, each having a stepform in which 2n layers form one stage, wherein n is a natural number of2 or higher, and the cell structure is located between the n first padstructures and the n second pad structures so that the first padstructures and the second pad structures are asymmetrical about the cellstructure and have asymmetrical step forms having different heights. 2.The semiconductor device of claim 1, wherein: a step of one layer existsbetween first pad structures adjacent to each other, a step of one layerexists between second pad structures adjacent to each other, and a stepof n layers exists between a pair of the first pad structures and thesecond pad structures placed on opposite sides of the cell structure. 3.The semiconductor device of claim 1, wherein the first and the secondpad structures are patterned in a step form having a step extended in adirection away from the cell structure, such that steps of each of thefirst and the second pad structures descend as the first and second padstructures extend away from the cell structure.
 4. The semiconductordevice of claim 1, wherein each layers of the first and the second padstructures comprises a first interlayer insulating layer and a firstconductive layer.
 5. The semiconductor device of claim 4, wherein: thecell structure comprises second interlayer insulating layers and secondconductive layers which are alternately stacked, the first interlayerinsulating layer and the second interlayer insulating layer formed, at asubstantially same level, are coupled, and the first conductive layerand the second conductive layer, formed at a substantially same level,are coupled.
 6. The semiconductor device of claim 1, wherein the cellstructure comprises: first channel layers configured to penetrate thecell structure; and at least one layer of a lower selection line,multiple layers of word lines, and at least one layer of upper selectionlines which are sequentially stacked and configured to surround thefirst channel layers.
 7. The semiconductor device of claim 6, furthercomprising a substrate comprising a source region coupled to a bottom ofthe first channel layers.
 8. The semiconductor device of claim 6,further comprising: a first source layer formed under the cellstructure; second source layers formed within the first source layer andcoupled to a bottom of the first channel layers; a memory layerconfigured to surround outer surfaces of the first channel layers andthe second source layers; and third source layers formed within thesecond source layers, respectively, configured to penetrate the secondsource layers and the memory layer, and coupled to the first sourcelayer.
 9. The semiconductor device of claim 6, further comprising: aninsulating layer formed under the cell structure; a first source layerformed within the insulating layer and coupled to a bottom of the firstchannel layers; second source layers formed within the first sourcelayer; and a memory layer configured to surround outer surfaces of thefirst channel layers and the first source layer.
 10. A semiconductordevice comprising: a cell structure; a first pad structure formed on oneside of the cell structure and configured to have a step form in which2n layers form one stage; a second pad structure formed on an oppositeside of the cell structure and configured to have a step form in which2n layers form one stage, wherein n is a natural number of 1 or higher,a step of n layers exists between the first pad structure and the secondpad structure, a third pad structure formed on the one side of the cellstructure and configured to have a step form in which 2n layers form onestage, wherein a step of one layer exists between the first padstructure and the third pad structure; and a fourth pad structure formedon the opposite side of the cell structure and configured to have a stepform in which 2n layers form one stage, wherein a step of one layerexists between the second pad structure and the fourth pad structure,wherein a step of n layers exists between the third pad structure andthe fourth pad structure.
 11. A semiconductor device, comprising: a cellstructure; a first pad structure formed on one side of the cellstructure and configured to have a step form in which 2n layers form onestage; and a second pad structure formed on an opposite side of the cellstructure and configured to have a step form in which 2n layers form onestage, wherein n is a natural number of 1 or higher, a step of n layersexists between the first pad structure and the second pad structure,wherein the first and the second pad structures are patterned in a stepform having a step extended in a direction away from the cell structure,such that steps of each of the first and the second pad structuresdescend as the first and second pad structures extend away from the cellstructure.